Pesticide tolerance in amphibians: induced tolerance in susceptible populations, constitutive tolerance in tolerant populations

Abstract

The role of plasticity in shaping adaptations is important to understanding the expression of traits within individuals and the evolution of populations. With increasing human impacts on the environment, one challenge is to consider how plasticity shapes responses to anthropogenic stressors such as contaminants. To our knowledge, only one study (using mosquitoes) has considered the possibility of induced insecticide tolerance. Using populations of wood frogs (Lithobates sylvaticus) located close to and far from agricultural fields, we discovered that exposing some populations of embryos and hatchlings to sublethal concentrations of the insecticide carbaryl induced higher tolerance to a subsequent lethal concentration later in life. Interestingly, the inducible populations were located >800 m from agricultural areas and were the most susceptible to the insecticide. In contrast, the noninducible populations were located close to agricultural areas and were the least susceptible. We also found that sublethal concentrations of carbaryl induced higher tadpole AChE concentrations in several cases. This is the first study to demonstrate inducible tolerance in a vertebrate species and the pattern of inducible and constitutive tolerance among populations suggests the process of genetic assimilation.

Amphibian population genetics in agricultural landscapes: does viniculture drive the population structuring of the European common frog (Rana temporaria)?

“…Also, some level of pesticide tolerance for amphibians from agricultural breeding pond populations was detected (Hua, Morehouse & Relyea, 2013; Hua et al, 2015). Yet such findings should not be generalized, since tested taxa and pesticides were limited, and pesticides still may cause lethal or sublethal effects on amphibians, depending on the path of exposure, exposure level and amphibian life stage.…”

The interplay between plasticity and evolution in response to human-induced environmental change

“…By quantifying both evolved and inducible (i.e . plastic) tolerances of wood frog populations varying in their distance from agriculture to an insecticide, Hua and colleagues found that evolved tolerance to a potentially lethal exposure of insecticide decreased with distance from agriculture 76, 79 . In contrast, the degree of plastic tolerance induced from an initial sublethal exposure increased with distance from agriculture 76 .…”

Evolved pesticide tolerance in amphibians: Predicting mechanisms based on pesticide novelty and mode of action

“…Our experimental units were 100-mL, glass Petri dishes filled with either 70 mL of water (control) or 70 mL of the lethal carbaryl, malathion, cypermethrin, imidacloprid, and thiamethoxam solutions. Because our objective for the TTD assays was to cause moderate mortality over time (Newman, 2010), we chose different lethal concentrations for each pesticide based on past studies (Hua et al, 2013b) and pilot data; the concentrations were as follows: carbaryl ¼ 25 mg/L, malathion ¼ 9.5 mg/L, cypermethrin ¼ 30 mg/L, permethrin ¼ 40 mg/L, imidacloprid ¼ 95 mg/L, and thiamethoxam ¼ 38 mg/L. The expectation is that TTD assays, which use relatively high concentrations to assess the relative sensitivities to different insecticides, provide information regarding sublethal effects (Newman, 2010).…”